The present invention is directed to an electrostatic chuck for holding, and maintaining substantially uniform temperatures across a substrate during processing of the substrate, and for increasing the life of the chuck in erosive process environments.
In semiconductor fabrication processes, electrostatic chucks are used to hold substrates for processing of the substrate. Electrostatic chucks are particularly useful in vacuum processing environments where there is insufficient differential pressure to hold the substrate using a vacuum chuck. A typical electrostatic chuck comprises an electrostatic member supported by a support adapted to be secured in a process chamber. The electrostatic member comprises an electrically insulated electrode. An electrical connector electrically connects the electrode to a voltage supply source in the process chamber. When the electrode is electrically biased with respect to the substrate held on the chuck, opposing electrostatic charge accumulates in the electrode and substrate, resulting in attractive electrostatic forces that hold the substrate to the chuck. Electrostatic chucks are generally described in, for example U.S. patent application Ser. Nos. 08/278,787 by Cameron, et al.; 08/276,735 by Shamouilian, et al.; and 08/189,562, by Shamouilian, et al.--all of which are incorporated herein by reference.
Conventional electrostatic chucks can also have temperature controlling systems to regulate the temperatures across the substrate held on the chuck. However, conventional temperature controlling systems often do not maintain uniform temperatures across the substrate, particularly at the perimeter or edge of the substrate. Excessively high temperatures at portions of the substrate can damage the integrated circuit chips formed on the substrate, and low temperatures can result in non-uniform processing of the substrate.
A typical conventional temperature controlling system functions by introducing a heat transfer fluid, such as helium, below the substrate via a single central aperture in the chuck. The single central aperture is often used to supply helium to recessed cavities below the substrate, such as an open trough or pattern of interconnected grooves, to distribute helium below the substrate. The trough or patterned grooves often stop short of the perimeter of the chuck forming a relatively large edge gap between the trough edges, or groove tips, and the perimeter of the substrate held on the electrostatic member, the gap often exceeding 10 to 20 mm. The large edge gap is provided to allow the overlying perimeter of the substrate to cover and seal the trough or grooves so that the heat transfer fluid does not leak out into the process environment. However, because no heat transfer fluid is held below the perimeter of the substrate overlying the edge gap, the temperature of the substrate perimeter is controlled less effectively compared to central portions of the substrate, resulting in non-uniform temperatures across the substrate.
Conversely, extending the edges of the trough or tips of the grooves all the way to the perimeter of the chuck causes other problems. The small gap between the trough edges, or groove tips, and the overlying substrate perimeter, can result in excessive leakage of helium at portions of the trough edges or groove tips. The accompanying reduction in temperature control of the overlying portions of the substrate perimeter, causes the substrate to exhibit hot or cold spots, and results in reduced yields of integrated circuits formed on the substrate.
Another limitation of conventional chucks results from the structure of the electrostatic member 10 of the chuck 11, which typically comprises a copper electrode layer 12 sandwiched between two polymer insulator layers 13a, 13b as shown in FIG. 1. The polymer layers 13a, 13b overlap beyond the edge of the copper electrode 12 at an outer periphery 14 of the electrostatic member to electrically insulate and seal the electrode 12. Typically, the overlapping portions of the polymer layers form a lower annular step 15 of approximately 0.5 to 2 mm, and more typically 1.25 to 1.50 mm width around the circumference of the raised electrode 12. The annular step 15 has several detrimental effects on the electrostatic chuck 11. First, because of the annular step 15, only a small portion of the outer periphery 14 of the electrostatic member 10 contacts the perimeter 16 of the substrate 17 beyond the circumference of the electrode 12. As a result, there is an increased probability of helium leakage from groove tips 18 near the outer periphery 14 contributing to excessive overheating of the substrate 17. A second effect is that the relatively small width of polymer insulator 10 separating the circumference of the electrode 12 from the process environment can cause a higher failure rate of the chuck 11, because the small insulator portion 19 can be rapidly eroded by the erosive process environment, exposing the electrode 12 and causing short-circuiting of the chuck 11. Erosion of insulator portion 19 is particularly rapid in oxygen or halogen containing gases and plasmas, which are used for a variety of tasks, such as for example, etching of substrates and cleaning of process chambers. Failure of the chuck during processing of the substrate can damage the substrate, and necessitates frequent replacement of short-circuited chucks.
Thus, it is desirable to have an electrostatic chuck having a temperature controlling system that allows maintaining substantially uniform temperatures across the substrate, and in particular the perimeter of the substrate, to provide higher integrated circuit chip yields from the substrate. It is also desirable to have an electrostatic chuck which demonstrates improved erosion resistance, and reduced failure rates, in erosive process environments.